With the emerging use of Internet "Web-Browsing", encapsulation of images within Web pages has become very common. However, in many situations such as art museums' home pages, navigation simulations, aerial imaging and medical archives, the standard technologies do not provide proper and efficient solutions. This is because high-resolution, high quality digital images are required which demand heavy traffic over the network and high processing power in the client machine.
Moreover, it is rarely possible to view the complete image at high resolution owing to the limited size of computer display monitors. Consider, by way of example, a museum home page allowing a visitor on the Web to view artwork on display at the museum. The artwork is stored on the Web server as a series of graphic files each derived by scanning the respective artwork at very high resolution. The resulting graphics files typically contain several millions of pixels whilst the highest quality display monitors currently available rarely have a resolution greater than 1000.times.1000 pixels. Thus, in order to download the whole image from the server, some of the high resolution inherent in the original graphic image must be sacrificed.
Frequently, however, it is not necessary to view the whole image at high resolution. Typically, a visitor to the Web site is content to view the complete image at relatively low-resolution providing that it is possible to select sections thereof for viewing at the highest resolution inherent in the original image stored on the Web server. This requirement has been addressed in the art, but with only limited success. Thus, a Web Site is known having the access name "www.ZoomMagic.com" in which images are stored on a Web server using the Photo CD file format which is proprietary to the Kodak Company. When a user accesses the Web site, various vignettes are displayed as miniature low-resolution images. Clicking on one of the images with the mouse, results in the selected image being displayed at full size at higher resolution in an area of the display presented as a TV screen having control buttons for allowing zooming and shifting as well as image cropping.
Zooming is achieved by clicking on the zoom button, whereupon the image is magnified by a predetermined factor, typically x2. In order to magnify the image more than this, the zoom button must be clicked again so as to allow the image to be successively magnified by the same magnification ratio, up to a predetermined maximum permitted zoom ratio. If, having thus magnified the image, the user is interested in a section of the image that is off-screen, then the image can be shifted by clicking on appropriate control buttons. The displayed image can also be cropped so as to remove sections thereof that are of no interest and may be distracting. Cropping is achieved by defining a window in the displayed image, whereupon the peripheral image surrounding the window is replaced by non-image data bearing no resemblance to the original image.
Such an approach suffers from several drawbacks. The Photo CD file format of the graphic images stored on the server is not provided in commonly available Web Browsers and therefore the necessary decompression algorithms must also be downloaded to the client. This adds to the overhead and increases the response time.
Furthermore, the manner in which zooming is performed is inflexible and cumbersome. Specifically, only predetermined zoom ratios are possible and integer multiples thereof can be obtained only by repeated zooming in discrete stages. Fine-tuning of the displayed image so as to display off-image sections thereof requires shifting the image after it has been magnified and this further adds to the processing overhead.
These drawbacks result in sluggish performance whereby the initial connection time is slow owing to the need to download proprietary decompression algorithms. Moreover, zooming in on a required section of the image is generally not amenable to a single operation thus requiring repeated graphic processing with the consequent time overhead. Furthermore, whilst image processing is being performed by the client software, the original size image remains intact, there being no pictorial feedback to the user that anything is happening even in the background. It may thus appear to the user that the system has crashed or that the software is defective, possibly resulting in his aborting the program. Bearing in mind that, the client-server communication to provide high-resolution image data imposes a significant time overhead, the lack of feedback is a serious source of frustration.
Many of the above limitations are characteristic of prior art approaches which rely on local processing by the client of image data downloaded from the Web server. Typically, standard compressed image formats such as JPEG are used, thus obviating the need to download proprietary decompression algorithms since the necessary decompression algorithm is already provided in the client's Web browser software. However, since the whole of the graphic image still requires downloading and local processing by the client is mandatory in order to effect the required zooming, prior art approaches are inherently sluggish in performance.